The following disclosure generally relates to electrical circuits and signal processing.
Conventional solid-state integrated circuits make use of reference voltage and reference current generation circuits for various purposes, for example, to provide dc biasing. Integrated circuits associated with applications having low tolerances to variations of a reference voltage or a reference current typically include accurate off-chip passive components for reference generation.
One type of reference voltage generation circuit is a bandgap circuit. A bandgap circuit typically generates a constant bandgap voltage (VBG) that is insensitive to conditions of an integrated circuit such as temperature, chip supply voltage, and fabrication process variations. Another type of reference voltage generation circuit is a proportional-to-absolute-temperature reference (PTAT) circuit. In contrast to a bandgap circuit, a PTAT circuit generates a PTAT voltage (VPTAT) that has a linear dependence on temperature (i.e., VPTAT=kT, where T represents absolute temperature (in Kelvin) and k represents a temperature insensitive constant). Since a transconductance (gm) of transistors (e.g., bipolar junction transistors) typically changes linearly with respect to temperature, some integrated circuits may need a current (i.e., IPTAT), proportional to voltage VPTAT, to bias one or more transistors in a manner that maintains a fixed transconductance for the transistors.
With respect to reference current generation circuits, process variations between integrated circuits typically prevent conventional integrated circuits from internally generating a sufficiently accurate reference current. For example, an internal reference current derived from an internal resistor (RCHIP) within one integrated circuit (e.g., VPTAT/RCHIP) may vary by ±15% or more relative to an internal reference current derived from an internal resistance RCHIP within a different integrated circuit having an exact same configuration. Such variations are not suitable for many high-precision, high-speed and high-bandwidth applications.
An integrated circuit requiring an accurate reference current can be produced using a reference voltage (e.g., VPTAT or VBG) and an external, more accurate resistance (REXT). Such a reference current requires a separate terminal connection and an additional external resistor. Additional terminals and resistors are generally expensive (i.e., terminals on an integrated circuit are an expense and require additional manufacturing cost to produce and, similarly, additional external components add to the cost of a given circuit with attending cost increases due to mounting and coupling the external component). Further, terminals also consume valuable die area and increase package size (i.e., unnecessary terminals waste valuable resource space).
FIG. 1 is a schematic diagram illustrating a conventional current generation circuit 100 including an integrated circuit 110. Integrated circuit 110 includes an external resistance REXT1 130 in communication with a source 132 through a terminal 131. Source 132 produces a first reference current (IREF1). Integrated circuit 110 also includes an external resistance REXT2 120 in communication with a source 122 through a terminal 121. Source 122 produces a second reference current (IREF2). The first and second reference currents IREF1, IREF2 can supply constant currents to various components on integrated circuit 110 such as circuit components 111a and 111b, respectively.